1. Field of the invention
The invention relates to electronic circuits, and more particularly, to an apparatus and method for detecting LED short circuit.
2. Description of the Related Art
A display panel is applied to many kinds of electronic products recently, such as a digital TV, a digital monitor, a smart phone, a notebook, a tablet PC . . . etc. A display panel includes a backlight device for providing lights to display images. Currently, a plurality of light emitting diodes (LEDs) are used as a light source of a common backlight device. Usually, the LEDs are connected into four LED strings or eight LED strings and the display panel controls its backlight by controlling each of the LED strings.
In general, a traditional LED short detection method applied to a backlight controller of the backlight device is to detect a cathode voltage (ISEN) of a LED string. When a LED string has a short circuit, a voltage across the LED string is reduced so that the cathode voltage (ISEN) of the LED string is increased. Thus the number of short circuits of a LED string can be obtained by detecting a cathode voltage (ISEN) of a LED string. However, a voltage across a LED string is usually 30˜60 volts. Due to the high across voltage (30˜60 volts), a traditional LED short detection circuit needs to be implemented by a high-voltage process to achieve a function of detecting the number of short circuits in a LED string. Therefore a traditional LED short detection circuit based on a high-voltage process can not be integrated into an integrated circuit based on a normal low-voltage process, especially for a system on chip (SOC).
Further a backlight controller is used to control luminance of LEDs. In general, the larger the size of a display panel, the more the number of LED strings or the more the number of LEDs in each LED string are set in the display panel. If fewer pins of a backlight controller are enough to perform a LED short detection on a LED string, it can save the cost of pins of the backlight controller. On the contrary, if more pins of a backlight controller are needed to perform a LED short detection on a LED string, the number of pins of the backlight controller is increased so as to increase production cost.
Since there are problems with a traditional LED short detection method, the present invention provides an apparatus and method for detecting LEDs short circuit to overcome the above mentioned problems.